Thermosetting powder compositions for coatings

ABSTRACT

The present invention relates to an isophthalic acid rich carboxyl functionalised polyester, containing linear chain aliphatic (poly)ether diols, and to thermosetting powder compositions comprising a mixture of the polyester with a β-hydroxylkylamide group containing cross-linking agent. The invention also relates to the use of said compositions for the preparation of powdered paints and varnishes for the making of coatings and to coatings obtained therewith.

The present invention relates to an isophthalic acid rich carboxylfunctionalised polyester, containing linear chain aliphatic (poly)etherdiols, and to thermosetting powder compositions comprising a mixture ofthe polyester with a hydroxyalkylamide group containing cross-linkingagent.

The invention also relates to the use of said compositions for thepreparation of powdered paints and varnishes for the making of coatingsand to coatings obtained therewith.

Thermosetting powder compositions are well known in the art and arewidely used as paints and varnishes for coating the most variousarticles. The advantages of these powder coatings are numerous; on theone hand, the problems associated with solvents are completelyeliminated, and on the other hand, the powders are used without any losssince only the powder in direct contact with the substrate is retainedon the article, the excess powder being, in principle, entirelyrecoverable and reusable. For these and other reasons, the powdercoating compositions are preferred to coating compositions in the formof solutions in organic solvents.

Thermosetting powder compositions have already been widely used in thecoating of domestic electrical appliances, automobile industryaccessories, and the like. They generally contain a thermosettingorganic binder, fillers, pigments, catalysts and various additives usedto adapt their properties to their intended use.

There are various types of thermosetting powder compositions. The bestknown compositions contain either a mixture of carboxyl group-containingpolymers, such as a carboxyl group-containing polyester or polyacrylate,and epoxy compounds, such as triglycidyl isocyanurate, glycidylgroup-containing acrylic copolymers or β-hydroxyalkylamides or a mixtureof hydroxyl group-containing polymers, most often a hydroxylgroup-containing polyester, with blocked or non-blocked isocyanates,melamine resins, and the like.

The carboxyl group-containing or the hydroxyl group-containingpolyesters suitable for use in the preparation of powdered varnishes andpaints have already been described in numerous publications such asarticles and patents. These polyesters are usually prepared fromaromatic dicarboxylic acids, mainly terephthalic acid and isophthalicacid and optionally a minor proportion of aliphatic or cycloaliphaticdicarboxylic acids, and from various polyols such as ethylene glycol,neopentyl glycol, 1,6-hexanediol, trimethylolpropane, and the like.

These polyesters based on aromatic dicarboxylic acids, when they areused with an appropriate cross-linking agent, provide thermosettingcompositions giving paint and varnish coatings possessing goodproperties, both as regards their appearance and as regards theirmechanical properties such as impact resistance, flexibility, etc.

Some of these polyesters and the powders derived from them often areused because of their remarkable weatherability characteristics. Thesepolyesters mostly are derived from isophthalic acid, being the mostimportant acid constituent among others and are commonly used withtriglycidyl isocyanurate (TGIC) as the cross-linking agent. Yet, thecoatings obtained from these powders, though proving outstandingweatherability, do not have any flexibility at all.

Moreover, TGIC presents problems of health and security. Indeed, TGIC isrelatively toxic (Rat Oral LD50 of 0.4 g/kg) and is mutagenic accordingto the Ames Mutagenicity Test.

As a non toxic alternative to TGIC, β-hydroxyalkylamides β-(HAA) havebeen used for the cross-linking of powders containing carboxyl-bearingpolyesters. But the use of β-(HAA) brings about new problems due to itshigh reactivity and to the fact that water is liberated during it'sreaction with carboxyl groups.

Powder paints comprising as a binder a carboxylic acid group containingpolyester and a β-(HAA) group containing cross-linking agent, producewater upon curing, thus creating bubbles in the coating especially whenrelatively thick layers are applied. Gas bubbles remaining in thecoating reduce the adherence and the protective effect of the coating.In order to reduce or even avoid these gas bubbles remaining in thecoating, two solutions, being either reducing the melt viscosity of thepowder, or slackening the reactivity of the binder system can beenvisaged. Yet, incorporation of considerable amounts of plasticisingconstituents in the binder system often reduces outdoor durability ofthe cured paint. Besides, from literature it is known that theesterification reaction of a resin acid group with a hydroxyl group ofthe β-(HAA) group containing hardener neither can be accelerated nor canbe slowed down, except from respectively increasing or decreasing theresin acid number along with the stoichiometric amount of the β-(HAA)group containing compound.

Some solutions have been sought for resolving these problems appearingwith the use of β-(HAA), and at the same time, for resolving theproblems of lack of flexibility of coatings made from powders containingisophthalic-rich polyesters.

EP 649890 claims powder coating compositions comprising a β-(HAA)cross-linking agent and an acid functional polyester having an acidnumber ranging from 15 through 70 mg KOH/g which is substantially basedon dicarboxylic acid units containing 80 to 100% mole of isophthalicacid, on glycols containing at least 50% mole of branched aliphaticglycols with at least 4 carbon atoms, at most 50% mole of a linearaliphatic diol with less than 4 carbon atoms and/or cycloaliphaticdiols, 0 to 10% mole of a linear aliphatic diol with at least 4 carbonatoms and on monomers having a functionality of at least three, in anamount of up to 8% mole based on the total amount of dicarboxylic acidsand glycols.

As appears from the examples, only a very few powders of this inventiongives a good flow on melting, which results in coatings having a poorsurface appearance.

A yet sophisticated way to flexibilise thermosetting powder coatingcompositions derived from carboxyl functional isophthalic acid richamorphous polyesters is the use of semi-crystaline acid functionalpolyesters as co-reactable part of the carboxylic acid amorphous resinin a binder along with a polyepoxy compound or a β-(HAA), such asclaimed in e.g. WO 91/14745. A careful selection of the propercombination of amorphous and semi-crystalline resins, respectively,enables for flexible and weatherable powder coating compositions derivedfrom carboxyl functional isophthalic acid rich polyesters, as far asparticular process conditions for mixing, extrusion and grinding areexercised and appropriate storage conditions of the powder thusobtained, are considered. Anyway, the solution presented in thisinvention to mix a semi-crystalline acid functional polyesters with acarboxyl functional amorphous poly-ester represents a technicalcomplication.

In patent application EP 668.895, thermosetting powders are describedwhich comprise a carboxyl group-containing polyester and a β-(HAA). Thepolyester may comprise isophthalic or terephthalic acid and has afunctionality less than 2, obtained by the addition in the polyester ofmonofunctional acids or alcohols. Due to the low functionality of thepolyester, its reactivity is reduced, which brings about a better flowduring the melting of the powder on the substrate. Nevertheless, as thepolyester has some non-reactive end groups, which do not participate inthe cross-linking reaction during the formation of the coating, thelatter has a reduced solvent resistance and a reduced flexibility.

In conclusion it can be seen that the various powdered compositionswhich have been proposed today for outdoor application where anoutstanding weatherability along with flexibility is required, and whichdo not make use of toxic cross-linking agents, all are characterised byone or more drawbacks or limitations. There is thus still a need forpowdered thermosetting compositions capable of producing coatingsproving an outstanding weatherability and a good flexibility and notexhibiting the shortcomings of prior art.

It now has been surprisingly found that, upon application and curing,the powder coating compositions, comprising the binder of the presentinvention,—based on a carboxylic acid group containing amorphousisophthalic acid/linear chain aliphatic (poly)ether diol rich polyesterin combination with a β-hydroxyalkylamide group containing cross-linkingagent—give paint films proving outstanding degassing properties at afilm thickness of up to about 200 μm for a curing time of from 15seconds to 50 minutes at curing temperatures from 140 to 250° C.Moreover, the powdered thermosetting compositions of the inventionproduce coatings proving very smooth coatings, exhibiting good outdoordurability and flexibility, without any defects possibly originated fromvolatile compounds.

As used in this specification, the expression “(poly)ether diol” meansthat these molecules may comprise only one ether group, such as indiethylene glycol, or several ether groups, such as in triethyleneglycol.

Thus, the present invention relates to a carboxylic acid groupcontaining amorphous polyester having an acid number of from 12 to 50 mgKOH/g and prepared from a polyacid constituent comprising from 85 to100% mole of isophthalic acid and from 0 to 15% mole of anotheraliphatic, cycloaliphatic or aromatic polyacid, and of a polyolconstituent comprising from 5 to 40% mole of one or more linear chainaliphatic (poly)ether diol, from 60 to 95% mole of neopentyl glycol andfrom 0 to 30% mole of another aliphatic and/or cycloaliphatic polyol.

The carboxyl functional amorphous polyester of the present invention ispreferably further characterised by:

-   -   a number averaged molecular weight ranging from 2500 to 8600,        more preferably from 3300 to 7500 as measured by gel permeation        chromatography (GPC)    -   a glass transition temperature Tg from 40 to 80° C. and more        preferably from 56 to 70° C. as measured by differential        scanning calorimetry (DSC) according to ASTM D3418 with a        heating gradient of 20° C. per minute    -   an ICI (cone/plate) viscosity accordingly to ASTM D4287,        measured at 200° C. ranging from 5 to 15000 mPa·s

The acid constituent of the amorphous polyester according to the presentinvention, is for 85 to 100% mole composed of isophthalic acid and for 0to 15% mole of another polyacid constituent selected from one or morealiphatic, cycloaliphatic or aromatic polyacids, such as fumaric acid,maleic acid, phthalic acid, terephthalic acid,1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid,1,2-cyclohexanedicarboxylic acid, succinic acid, adipic acid, glutaricacid, pimelic acid, suberic acid, azelaic acid, sebacic acid,1,12-dodecanedioic acid, trimellitic acid, pyromellitic acid, and thecorresponding anhydrides.

The polyol constituent of the amorphous polyester according to thepresent invention, is for 5 to 40% mole composed of a linear chainaliphatic (poly)ether diol such as diethylene glycol, dipropyleneglycol, triethylene glycol and tripropylene glycol, used in a mixture oralone. The polyol constituent of this polyester also comprises 60 to 95%mole of neopentyl glycol and for 0 to 30% mole and preferably for 0 to20% mole of another polyol constituent selected from one or morealiphatic or cycloaliphatic polyol such as ethylene glycol, propyleneglycol, 1,6-hexanediol, 1,4cyclohexanediol, 1,4-cyclohexanedimethanol,hydrogenated Bisphenol A, 2-methyl-1,3-propanediol,2-butyl-2-ethyl-1,3-propanediol, neopentyl glycol hydroxypivalate,trimethylolpropane, ditrimethylolpropane, pentaerythrytol, etc.

Preferably, neopentyl glycol hydroxypivalate is not used as polyol inthe amorphous polyester according to the present invention.

Preferably, the polyester according to the present invention is composedof polycarboxylic acid units containing from 85 to 100% mole ofisophthalic acid, from 0 to 15% mole of terephthalic acid and/or1,4-cyclohexanedicarboxylic acid, and of polyol constituents containingfrom 5 to 40% mole of linear chain aliphatic (poly)ether diol,preferably diethylene glycol, from 60 to 95% mole of neopentyl glycoland from 0 to 30% mole of ethylene glycol, propylene glycol,1,6-hexanediol, trimethylolpropane or pentaerythrytol.

The carboxylic acid group containing amorphous polyester, according tothe present invention, is usually prepared using conventionalesterification techniques well known in the art. The polyester isgenerally prepared according to a procedure consisting of one or morereaction steps.

The esterification conditions generally used to prepare the polyestersare conventional, namely a standard esterification catalyst, such asdibutyltin oxide, dibutyltin dilaurate, n-butyltin trioctoate, sulphuricacid or a sulphonic acid, tetraisopropyl titanate or tetra-n-butyltitanate can be used in an amount from 0.05 to 1.50% by weight of thereactants and optionally, colour stabilisers, for example, phenolicantioxidants such as Irganox 1010 (Ciba) or phosphonite- andphosphite-type stabilisers such as tributylphosphite, can be added in anamount from 0 to 1% by weight of the reactants.

Polyesterification is generally carried out at a temperature which isgradually increased from 130° C. to about 190 to 250° C., first undernormal pressure, then, when necessary, under reduced pressure at the endof each process step, while maintaining these operating conditions untila polyester is obtained, which has the desired hydroxyl and/or acidnumber. The degree of esterification is generally followed bydetermining the amount of water formed in the course of the reaction andthe properties of the obtained polyester, for example the hydroxylnumber, the acid number, the molecular weight or the viscosity.

The present invention also relates to powdered thermosettingcompositions for coatings, characterised in that they comprise:

a) a carboxylic acid group containing amorphous polyester as definedabove, and

b) a cross-linking agent having at least two β-hydroxyalkylamide groups.

The carboxyl group containing amorphous polyester, as described above,is part of a binder system along with a β-hydroxyalkylamide groupcontaining cross-linking agent, in the preparation of powder coatingcompositions for use as paint or clear lacquer.

It has been found that polyesters containing more than 85% mole ofisophthalic acid, along with the other constituents of the polyester,give especially good coatings when crosslinked with β-(HAA).

Suitable β-hydroxyalkylamide cross-linking agents are those whichcontain at least two bis(β-hydroxyalkyl)amide groups. Commercialproducts are available, such asN,N,N′,N′-tetrakis-(2-hydroxyethyl)-adipamide, known under the tradenamePrimid XL-552 and N,N,N′,N′-tetrakis-(2-hydroxypropyl)-adipamide, knownunder the tradename Primid QM1260 for example. Other β-hydroxyalkylamideare described in the literature, for example those mentioned in thepatents U.S. Pat. No. 4,727,111, U.S. Pat. No. 4,788,255, U.S. Pat. No.4,076,917, or in the patent applications EP-A-322834 and EP-A-473380.

The β-hydroxyalkylamide group containing cross-linking agent describedherein above is generally used in an amount from 0.25 to 1.40 preferablyfrom 0.60 to 1.05 equivalent of carboxyl group present in the amorphouspolyester per equivalent of β-hydroxyalkyl groups.

The amount of cross-linking agent in the powdered thermosettingcompositions according to the present invention is generally from 1 to10% by weight relative to the weight of the carboxylic acid containingamorphous polyester.

The powdered thermosetting compositions for coatings according to thepresent invention preferably contain less than 5% by weight ofsemi-crystalline polyester. The powdered thermosetting compositions forcoatings according to the present invention more preferably contain nosemi-crystalline polyester.

In addition to the essential components described above, compositionswithin the scope of the present invention can also include flow controlagents such as Resiflow PV5 (Worlee), Modaflow (Monsanto), Acronal 4F(BASF), etc., and degassing agents such as benzoin (BASF) etc. To theformulation UV-light absorbers such as Tinuvin 900 (Ciba), hinderedamine light stabilisers represented by Tinuvin 144 (Ciba), otherstabilising agents such as Tinuvin 312 and 1130 (Ciba), antioxidantssuch as Irganox 1010 (Ciba) and stabilisers from the phosphonite orphosphate type can be added.

Both, pigmented systems as well as clear lacquers can be prepared.

A variety of dyes and pigments can be utilised in the composition ofthis invention. Examples of useful pigments and dyes are: metallicoxides such as titaniumdioxide, ironoxide, zincoxide and the like, metalhydroxides, metal powders, sulphides, sulphates, carbonates, silicatessuch as ammoniumsilicate, carbon black, talc, china clay, barytes, ironblues, leadblues, organic reds, organic maroons and the like.

The coating compositions according to the present invention generallycomprise:

-   -   from 50 to 98 weight % of carboxylic acid group containing        amorphous polyester    -   from 1 to 10 weight % of β-hydroxyalkylamide cross-linking agent    -   from 0 to 10 weight % of one or more UV light absorbers,        stabilisers, flow control agents, degassing agents    -   from 0 to 49 weight % pigments and/or dyes.

The components of the composition according to the invention may bemixed by dry blending in a mixer or blender (e.g. drum mixer). Thepremix is then homogenised at temperatures ranging from 70 to 150° C. ina single screw extruder such as the BUSS-Ko-Kneter or a double screwextruder such as the PRISM or APV. The extrudate, when cooled down, isgrounded to a powder with a particle size ranging from 10 to 150 μm. Thepowdered composition may be deposited on the substrate by use of apowder gun such as an electrostatic CORONA gun or TRIBO gun. On theother hand, well-known methods of powder deposition such as thefluidised bed technique can be used. After deposition the powder isheated to a temperature between 140 and 250° C., causing the particlesto flow and fuse together to form a smooth, uniform, continuous,uncratered coating on the substrate surface.

The following examples are submitted for a better understanding of theinvention without being restricted thereto.

EXAMPLE 1

A mixture of 357.0 parts of neopentyl glycol, 63.2 parts of diethyleneglycol and 8.8 parts of trimethylolpropane are placed in a conventionalfour neck round bottom flask equipped with a stirrer, a distillationcolumn connected to a water cooled condenser, an inlet for nitrogen anda thermometer attached to a thermoregulator. The flask contents areheated, while stirring under nitrogen, to a temperature of circa 130° C.at which point 715.5 parts of isophthalic acid and 2.5 parts ofn-butyltintrioctoate are added. The heating is continued gradually to atemperature of 230° C. Water is distilled from the reactor from 180° C.on. When distillation under atmospheric pressure stops, 1.0 part oftributylphosphite is added and a vacuum of 50 mm Hg is graduallyapplied. After three hours at 230° C. and 50 mm Hg, followingcharacteristics are obtained: AN 19 mg KOH/g OHN 3 mg KOH/gICI^(200° C.) (cone/plate) 6000 mPa · s Tg (DSC, 20°/min) 56° C.

EXAMPLE 2

Adopting the procedure of Example 1, another polyester is made using718.8 parts isophthalic acid, 360.4 parts neopentyl glycol and 63.6parts diethylene glycol. The obtained polyester has followingcharacteristics: AN 31 mg KOH/g ICI^(200° C.) (cone/plate) 1500 mPa · sTg (DSC, 20°/min) 56° C.

EXAMPLE 3

The polyesters as illustrated above, are then formulated to a powderaccordingly to one of the formulations as mentioned below. Formulation AFormulation B White paint formulation Brown paint formulation Binder69.06 Binder 78.33 Kronos 2310 29.60 Bayferrox 130 4.44 Resiflow PV50.99 Bayferrox 3950 13.80 Benzoin 0.35 Carbon Black FW2 1.09 ResiflowPV5 0.99 Benzoin 0.35

The powders are prepared first by dry blending of the differentcomponents and then by homogenisation in the melt using a PRISM 16 mmL/D 15/1 twin screw extruder at an extrusion temperature of 85° C. Thehomogenised mix is then cooled and grinded in an Alpine. Subsequentlythe powder is sieved to obtain a particle size between 10 and 110 μm.The powder thus obtained is deposited on cold rolled steel with athickness of 0.8 mm, by electrostatic deposition using theGEMA-Volstatic PCG 1 spraygun. At a film thickness of about 80 μm thepanels are transferred to an air-ventilated oven, where curing proceedsfor 15 minutes at a temperature of 200° C. The paint characteristics forthe finished coatings obtained from the polyesters of the presentinvention (Ex. 1 and 2) as well as from two commercial polyesters,Crylcoat 7617 and Crylcoat 7642, standard—Primid XL552 (95/5)—resins forrespectively outdoor and superdurable applications, and illustrated byway of comparison, are given in table 1. Crylcoat 7617 is mainlycomposed of terephthalic acid and neopentyl glycol and has an AN of 30mg KOH/g. Crylcoat 7642 is purely composed of isophthalic acid andneopentyl glycol and has an AN of 35 mg KOH/g.

In this table:

-   Column 1: indicates the identification number of the formulation-   Column 2: indicates the type of formulation    -   A=white (RAL9010)    -   B=medium brown (RAL8014)-   Column 3: indicates the type and quantity of the polyester resin    used in the formulation-   Column 4: indicates the type and quantity of β-hydroxyalkylamide    cross-linker:    -   XL552=Primid XL552        (EMS)=N,N,N′,N′-tetrakis-(2-hydroxyethyl)-adipamide-   Column 5: indicates the 60° gloss, measured according to ASTM D523-   Column 6: indicates the direct impact strength according to ASTM    D2794. The highest impact which does not crack the coating is    recorded in kg·cm.-   Column 7: indicates the reverse impact strength according to ASTM    D2794. The highest impact which does not crack the coating is    recorded in kg·cm.-   Column 8: indicates the Erichsen slow embossing according to    ISO 1520. The highest penetration which does not crack the coating    is recorded in mm.-   Column 9: indicates the aspect of the coating    -   g=very smooth mirror-like finish

m=orange peel TABLE 1 Powder Composition Erichsen Direct Reverse SlowVisual example Formulation Polyester hardener Gloss Impact ImpactEmbossing Aspect 4 A 1 (96.5) XL552 90 60 40 8.8 g/m (3.5) 5 A 2 (95)XL552 94 100 100 9.0 g (5) 6 B 2 (95) XL552 96 80 80 9.1 g (5) 7 B CC761XL552 90 120 120 9.2 m 7 (95) (5) 8 B CC764 XL552 91 0 0 3.2 m 2 (95)(5)

As clearly appears from table 2, the powders according to the presentinvention (Ex. 4 to 6) thus prove to satisfy a combination ofproperties, such as flexibility and gloss. They all give coatings with avery good surface aspect, comparable to nowadays standard outdoorpowders (Comparative example 7). As clearly appears from comparativeexample 8 no flexibility is obtained for a coating based on aβ-hydroxyalkylamide hardener and a carboxyl group containingisophthalic-rich polyester where no linear chain aliphatic (poly)etherdiol is used

Moreover it has been proven that polyester resins answering acomposition as claimed in this invention, allow for paint coatingwithout any defects or pinholing at a thickness of up to 200 μm. Thus,powder formulations answering the examples 4 to 6, allow for paint filmsof 200 μm with outstanding flow and without showing any pinhole or otherdefect.

As clearly appears from table 1, powder compositions according to thepresent invention containing as a binder a combination of the carboxylfunctional polyester according to the present invention along with aβ-hydroxyalkylamide cross-linking agent, prove upon application andcuring an unique combination of properties such as a good flexibility,outstanding flow and gloss.

Besides an outstanding flexibility, flow and degassing properties, thepowder coating compositions of the present invention prove to satisfy anexcellent outdoor resistance comparable to or better than the currentlyused nowadays commercial polyester based powders.

In table 2, the relative 60° gloss values, recorded every 400 hours,according to ASTM D523, is reported for the coating obtained fromexample 6, according to the invention, and submitted to the Q-UVaccelerated weathering test. In the same table are given, by way ofcomparison, the weathering results for the coatings obtained fromexample 7 and 8, derived from commercial resins. TABLE 2 UV-A (340 nm, I= 0.77 W/m²/nm Hours Ex. 6 Ex. 7 Ex. 8 0 100 100 100 400 99 99 99 800 9788 99 1200 98 74 97 1600 97 69 97 2000 100 63 95 2400 100 26 92 2800 10086 3200 97 80 3600 92 80 4000 85 73 4400 77 76 4800 68 69 5200 59 755600 51 66 6000 43 60 6400 54 6800 57 7200 71 7600 66 8000 50 8400 508800 47 9200 45 9600 43 10000 41 10400 39 10800 35 11200 33 11600 30

1. A carboxylic acid group containing amorphous polyester having an acidnumber of from 12 to 50 mg KOH/g and prepared from a polyacidconstituent comprising from 85 to 100% mole of isophthalic acid and from0 to 15% mole of another aliphatic, cycloaliphatic or aromatic polyacid,and of a polyol constituent comprising from 5 to 40% mole of one or morelinear chain aliphatic (poly)ether diol, from 95 to 60% mole ofneopentyl glycol and from 0 to 30% mole of another aliphatic and/orcycloaliphatic polyol.
 2. The carboxylic acid group containing polyesteraccording to claim 1, which is characterised by a number averagedmolecular weight ranging from 2500 to 8600, preferably from 3300 to 7500as measured by gel permeation chromatography (GPC) a glass transitiontemperature Tg from 40 to 80° C. and preferably from 56 to 70° C. asmeasured by differential scanning calorimetry (DSC) according to ASTMD3418 with a heating gradient of 20° C. per minute an ICI (cone/plate)viscosity accordingly to ASTM D4287, measured at 200° C. ranging from 5to 15000 mPa·s
 3. The carboxylic acid group containing polyesteraccording to claim 1 wherein the 0 to 15% mole of the aliphatic,cycloaliphatic or aromatic polyacids, other than isophthalic acid isselected from fumaric acid, maleic acid, phthalic acid, terephthalicacid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylicacid, 1,2-cyclohexanedicarboxylic acid, succinic acid, adipic acid,glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid,1,12-dodecanedioic acid, trimellitic acid, pyromellitic acid, and thecorresponding anhydrides.
 4. The carboxylic acid group containingpolyester according to claim 1 wherein the 5 to 40% mole of linear chainaliphatic (poly)ether diols are selected from diethylene glycol,dipropylene glycol, triethylene glycol and tripropylene glycol, used ina mixture or alone, and in that the 0 to 30% mole of the other aliphaticand/or cycloaliphatic diol is selected from ethylene glycol, propyleneglycol, 1,6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol,hydrogenated Bisphenol A, 2-methyl-1,3-propanediol,2-butyl-2-ethyl-1,3-propanediol, neopentyl glycol hydroxypivalate,trimethylolpropane, ditrimethylolpropane and pentaerythrytol, used in amixture or alone.
 5. The carboxylic acid group containing polyesteraccording to claim 1 which comprises a polyacid constituent comprisingfrom 85 to 100% mole of isophthalic acid and from 0 to 15% mole ofterephthalic acid and/or 1,4-cyclohexanedicarboxylic acid and of apolyol constituent comprising from 5 to 40% mole of linear chainaliphatic (poly)ether diol, preferably diethylene glycol, from 60 to 95%mole of neopentyl glycol and from 0 to 30% mole of ethylene glycol,propylene glycol, 1,6-hexanediol, trimethylolpropane or pentaerythrytol.6. Powdered thermosetting compositions, which comprise: a) a carboxylicacid group containing amorphous polyester according to any of thepreceding claims, b) a cross-linking agent having at least twoβ-hydroxyalkylamide groups.
 7. Powdered thermosetting compositionsaccording to claim 6, comprising: from 50 to 98 weight % of carboxylicacid group containing amorphous polyester from 1 to 10 weight % ofα-hydroxyalkylamide cross-linking agent from 0 to 10 weight % of one ormore UV light absorbers, stabilisers, flow control agents, degassingagents from 0 to 49 weight % pigments and/or dyes.
 8. Process forcoating an article, wherein powdered thermosetting compositions forcoatings according to claim 6 is applied by an electrostatic or frictioncharging gun, or in a fluidized bed, and in that the coating thusobtained is heated at a temperature of from 140 to 250° C.
 9. Substrateentirely or partially coated by the process of claim 8.